Method for synchronization in a local area network including a store-and-forward device
First Claim
1. A method for identifying inaccurate time measurements when running time synchronization on a local area network, the local area network comprising a sending device, a destination device and a switching device and/or a store-and-forward device arranged on a path between the sending device and the destination device, the method comprising:
- storing a value for an estimated relative local frequency deviation (dfR) and a confidence comparison value for a local time-of-day clock in a memory in the sending device;
obtaining a time value (tP) of the local time-of-day clock at a previous time adjustment;
obtaining an estimated local frequency accuracy (d2fR) at the previous time adjustment;
obtaining an estimated local time precision (dtP) at the previous time adjustment;
receiving time stamps;
calculating a new time adjustment (tA) from the received time stamps;
obtaining a time value (tR) of the local time-of-day clock for the new time adjustment (tA);
calculating an upper acceptance level (tH) and a lower acceptance level (tL) for the new time adjustment (tA) based on the following equations;
tH=tB+dtB
tL=tB−
dtB where tB=tP+(tR−
tP)*(1+dfR) anddtB=dtP+(tR−
tP)*d2fR; and
determining whether the new time adjustment (tA) falls between tH and tL.
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Accused Products
Abstract
The present invention relates to a method for identifying inaccurate time measurements in a local area network. The local area network comprises a sending device (2), such as a time client, a destination device (3), such as a timeserver, and a switching device and/or a store-and-forward device (6). A time request packet (4) is rejected if it arrives at the time client or timeserver within a given or calculated minimum distance from the preceding network packet. The time request packet (4) is also rejected if it falls outside a set of calculated error limits based on a set of estimates. Those estimates are kept in the time client memory and updated according to a given set of rules.
30 Citations
5 Claims
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1. A method for identifying inaccurate time measurements when running time synchronization on a local area network, the local area network comprising a sending device, a destination device and a switching device and/or a store-and-forward device arranged on a path between the sending device and the destination device, the method comprising:
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storing a value for an estimated relative local frequency deviation (dfR) and a confidence comparison value for a local time-of-day clock in a memory in the sending device; obtaining a time value (tP) of the local time-of-day clock at a previous time adjustment; obtaining an estimated local frequency accuracy (d2fR) at the previous time adjustment; obtaining an estimated local time precision (dtP) at the previous time adjustment; receiving time stamps; calculating a new time adjustment (tA) from the received time stamps; obtaining a time value (tR) of the local time-of-day clock for the new time adjustment (tA); calculating an upper acceptance level (tH) and a lower acceptance level (tL) for the new time adjustment (tA) based on the following equations;
tH=tB+dtB
tL=tB−
dtBwhere tB=tP+(tR−
tP)*(1+dfR) anddtB=dtP+(tR−
tP)*d2fR; anddetermining whether the new time adjustment (tA) falls between tH and tL. - View Dependent Claims (2, 3)
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4. A method for identifying inaccurate time measurements when running time synchronization on a local area network, the local area network comprising a sending device, a destination device and a switching device and/or a store-and-forward device connected between the sending device and the destination device, the method comprising:
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receiving a network packet and then a time request packet at the destination device; measuring the time between the received network packet and the received time request packet; and rejecting the received time request packet if the measured time is within a predetermined time interval, wherein the predetermined time interval is calculated using a known length of a time request packet and a required inter-packet gap. - View Dependent Claims (5)
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Specification